Effects of phorbol 12-myristate 13-acetate on potassium transport in the red blood cells of frog Rana temporaria.

Phorbol 12-myristate 13-acetate (PMA), a stimulator of PKC, was examined for its influence on K(+) ((86)Rb) influx in the frog erythrocyte. PMA, 0.1 microM, was found to accelerate ouabain-sensitive K(+) influx, which was suppressed by 73% with 1 mM amiloride, indicating secondary activation of the Na(+)-K(+)-pump due to stimulation of Na(+ )/H(+) exchange. PMA-induced stimulation of the sodium pump was completely inhibited with 1 microM staurosporine and by approximately 50% with 20 microM chelerythrine. In contrast to Na(+)-K(+)-pump, an activity of Cl(-)-dependent K(+) transport (K-Cl cotransport, KCC), calculated as the difference between K(+) influxes in Cl(-) and NO(3) (-)-media, was substantially decreased under the influence of PMA. Staurosporine fully restored the PMA-induced inhibition of KCC, whereas chelerythrine did not exert any influence. Osmotic swelling of the frog erythrocytes was accompanied by approximately twofold stimulation of KCC. Swelling-activated KCC was inhibited by approximately 50 and approximately 83% in the presence of PMA and genistein, respectively, but not chelerythrine. Exposure of the frog erythrocytes to 5 mM fluoride (F(-)) also reduced the KCC activity in isotonic and hypotonic media, with maximal suppression of K(+) influx in both media being observed upon simultaneous addition of PMA and F(-). Furosemide and [(dihydronindenyl)oxy] alkanoic acid inhibited the K(+) influx in both the media by approximately 50-60%. The results obtained show both the direct and indirect effects of PMA on the K(+) transport in frog erythrocytes and a complicated picture of KCC regulation in frog erythrocytes with involvement of PKC, tyrosine kinase and protein phosphatase.